That really isn't an option on that unit. It's possible but not something that a DIYer really would tackle.

Why do you want it cleaned?

Ah... Each defrost will drop a cup or more of water in there. It should dry by evaporation. If it isn't drying it can get nasty. If there isn't much airflow due to clearances around the unit that can hinder drying too.

Check that the grille in front is clear and the condenser is clear. The fan will usually move enough air through to dry the pan in between defrosts.

Beyond that you can carefully access from back and clean the pan. Unplug it so the fan doesn't bite you.